Method and system of doppler correction for mobile communications systems

• US 5,995,045 A
• Filed: 01/23/1998
• Issued: 11/30/1999
• Est. Priority Date: 07/15/1997
• Status: Expired due to Fees

• Current Assignee: Texas A&M University System
• Original Assignee: Texas A&M University System
• Inventors: Georghiades, Costas N., Spasojevic, Predrag
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US09/012,197
• Time in Patent Office: 676 Days
• Field of Search: 342/418, 342/357.03, 455/63, 455/296, 375/344, 375/348
• US Class Current: 342/418
• CPC Class Codes: H04B 7/01 Reducing phase shift

Abstract

Doppler correction system and method comprising receiving a Doppler effected signal comprising a preamble signal (32). A delayed preamble signal (48) may be generated based on the preamble signal (32). The preamble signal (32) may be multiplied by the delayed preamble signal (48) to generate an in-phase preamble signal (60). The in-phase preamble signal (60) may be filtered to generate a substantially constant in-phase preamble signal (62). A plurality of samples of the substantially constant in-phase preamble signal (62) may be accumulated. A phase-shifted signal (76) may also be generated based on the preamble signal (32). The phase-shifted signal (76) may be multiplied by the delayed preamble signal (48) to generate an out-of-phase preamble signal (80). The out-of-phase preamble signal (80) may be filtered to generate a substantially constant out-of-phase preamble signal (82). A plurality of samples of the substantially constant out-of-phase signal (82) may be accumulated. A sum of the in-phase preamble samples and a sum of the out-of-phase preamble samples may be normalized relative to each other to generate an in-phase Doppler estimator (92) and an out-of-phase Doppler estimator (94).

Claims

1. A method of estimating a Doppler offset of a signal, comprising the steps of:

receiving a Doppler effected signal comprising a preamble signal;

generating a delayed preamble signal based on the preamble signal;

multiplying the preamble signal by the delayed preamble signal to generate an in-phase preamble signal;

filtering the in-phase preamble signal to generate a substantially constant in-phase preamble signal;

accumulating a plurality of samples of the substantially constant in-phase preamble signal;

generating a phase-shifted preamble signal based on the preamble signal;

multiplying the phase-shifted preamble signal by the delayed preamble signal to generate an out-of-phase preamble signal;

filtering the out-of-phase preamble signal to generate a substantially constant out-of-phase preamble signal;

accumulating a plurality of samples of the substantially constant out-of-phase preamble signal; and

normalizing a sum of the in-phase preamble samples and a sum of the out-of-phase preamble samples relative to each other to generate an in-phase Doppler estimator and a out-of-phase Doppler estimator.

2. The method of claim 1, wherein the signal comprises a GMSK differentially detected signal.

3. The method of claim 1, wherein the preamble comprises a sequence of zeros.

4. The method of claim 1, wherein the preamble signal comprises a sequence of sixteen zeros.

5. The method of claim 1, wherein the preamble signal consists of a sequence of sixteen zeros.

6. The method of claim 1, wherein the delayed preamble signal comprises the preamble signal delayed by a two bit interval.

7. The method of claim 1, the step of filtering the in-phase preamble signal to generate the substantially constant in-phase preamble signal comprising the step of filtering high frequency components from the in-phase preamble signal.

8. The method of claim 7, the step of filtering the out-of-phase preamble signal to generate the substantially constant out-of-phase preamble signal comprising the step of filtering high frequency components from the out-of-phase preamble signal.

9. The method of claim 1, the step of accumulating the plurality of samples of the substantially constant in-phase preamble signal comprising the steps of:

periodically obtaining samples of the substantially constant in-phase preamble signal; and

summing the obtained in-phase preamble samples.

10. The method of claim 9, wherein the sampling period comprises one bit interval.

11. The method of claim 9, the step of accumulating the plurality of samples of the substantially constant out-of-phase preamble signal comprising the steps of:

periodically obtaining samples of the substantially constant out-of-phase preamble signal; and

summing the obtained out-of-phase preamble samples.

12. The method of claim 11, wherein the sampling period comprises one bit interval.

13. The method of claim 1, wherein the phase-shifted preamble signal is a quadrature signal of the preamble signal.

14. The method of claim 1, the step of generating the phase-shifted preamble signal based on the preamble signal comprising the step of applying a Hilbert transform to the preamble signal.

15. The method of claim 1, the step of normalizing the sum of the in-phase preamble samples and the sum of the out-of-phase preamble samples relative to each other further comprising the steps of:

dividing the sum of the in-phase preamble samples by the square root of the sum of the square of the in-phase preamble samples and the square of the out-of-phase preamble samples; and

dividing the sum of the out-of-phase preamble samples by the square root of the sum of the square of the out-of-phase preamble samples and the square of the in-phase preamble samples.

16. The method of claim 1, wherein the in-phase Doppler estimator comprises a sine of the Doppler offset and the out-of-phase Doppler estimator comprises a cosine of the Doppler offset.

17. A method of correcting for a Doppler offset of a signal, comprising the steps of:

receiving a Doppler effected signal comprising a preamble signal and a data signal;

generating a delayed preamble signal based on the preamble signal;

multiplying the preamble signal by the delayed preamble signal to generate an in-phase preamble signal;

filtering the in-phase preamble signal to generate a substantially constant in-phase preamble signal;

accumulating a plurality of samples of the substantially constant in-phase preamble signal;

generating a phase-shifted preamble signal based on the preamble signal;

multiplying the phase-shifted preamble signal by the delayed preamble signal to generate an out-of-phase preamble signal;

filtering the out-of-phase preamble signal to generate a substantially constant out-of-phase preamble signal;

accumulating a plurality of samples of the substantially constant out-of-phase preamble signal;

normalizing a sum of the in-phase preamble samples and a sum of the out-of-phase preamble samples relative to each other to generate an in-phase Doppler estimator and a out-of-phase Doppler estimator;

generating a delayed data signal based on the data signal;

multiplying the data signal by the delayed data signal to generate an in-phase data signal;

multiplying the in-phase data signal by the in-phase Doppler estimator to generate a Doppler corrected in-phase data signal;

generating a phase-shifted data signal based on the data signal;

multiplying the phase-shifted data signal by the delayed data signal to generate an out-of-phase data signal;

multiplying the out-of-phase data signal by the out-of-phase Doppler estimator to generate a Doppler corrected out-of-phase data signal; and

combining the Doppler corrected in-phase data signal and the Doppler corrected out-of-phase data signal to generate a Doppler corrected data signal.

18. The method of claim 17, wherein the signal comprises a GMSK differentially detected signal.

19. The method of claim 17, wherein the preamble signal comprises a sequence of zeros.

20. The method of claim 17, wherein the preamble signal comprises a sequence of sixteen zeros.

21. The method of claim 17, wherein the preamble signal consists of a sequence of sixteen zeros.

22. The method of claim 17, wherein the delayed preamble signal comprises the preamble signal delayed by two bit intervals and the delayed data signal comprises the data signal delayed by two bit intervals.

23. The method of claim 17, further comprising the step of filtering the in-phase data signal.

24. The method of claim 23, the step of filtering the in-phase preamble signal comprising the step of filtering high frequency components from the in-phase preamble signal and the step of filtering the in-phase data signal comprising the step of filtering high frequency components from the in-phase data signal.

25. The method of claim 17, further comprising the step of filtering the out-of-phase data signal.

26. The method of claim 25, the step of filtering the out-of-phase preamble signal comprising the step of filtering high frequency components from the out-of-phase preamble signal and the step of filtering the out-of-phase data signal comprising the step of filtering high frequency components from the out-of-phase data signal.

27. The method of claim 17, further comprising the step of filtering the Doppler corrected data signal.

28. The method of claim 27, the step of filtering the Doppler corrected data signal further comprising the step of filtering high frequency components from the Doppler corrected data signal.

29. The method of claim 17, wherein the phase-shifted preamble signal is a quadrature signal of the preamble signal and the phase-shifted data signal is a quadrature signal of the data signal.

30. The method of claim 17, the step of generating the phase-shifted preamble signal based on the preamble signal comprising the step of applying a Hilbert transform to the preamble signal and the step of generating the phase-shifted data signal based on the data signal comprising the step of applying a Hilbert transform to the data signal.

31. The method of claim 17, the step of normalizing the sum of the in-phase preamble samples and the sum of the out-of-phase preamble samples relative to each other further comprising the steps of:

dividing the sum of the in-phase preamble samples by the square root of the sum of the square of the in-phase preamble samples and the square of the out-of-phase preamble samples; and

dividing the sum of the out-of-phase preamble samples by the square root of the sum of the square of the out-of-phase preamble samples and the square of the in-phase preamble samples.

32. The method of claim 17, wherein the in-phase Doppler estimator comprises a sine of the Doppler offset and the out-of-phase Doppler estimator comprises a cosine of the Doppler offset.

33. A mobile communications system, comprising:

a first object comprising a transmitter to transmit a predefined preamble signal with a data signal;

a second object moving relative to the first object, the second comprising;

a receiver to receive the transmitted preamble signal and the data signal;

a Doppler estimation circuit comprising;

a delay channel coupled to the receiver to generate a delayed preamble signal based on the preamble signal;

an in-phase channel coupled to the receiver and the delay channel, comprising;

a first multiplier junction to multiply the preamble signal by the delayed preamble signal to generate an in-phase preamble signal;

a first filter to generate a substantially constant in-phase preamble signal;

a first accumulator to obtain a plurality of samples of the substantially constant in-phase preamble signal;

an out-of-phase channel coupled to the receiver and the delay channel, comprising;

a transform to generate a phase-shifted preamble signal based on the preamble signal;

a second multiplier junction to multiply the phase-shifted preamble signal by the delayed preamble signal to generate an out-of-phase preamble signal;

a second filter to generate a substantially constant out-of-phase preamble signal;

an second accumulator to obtain a plurality of samples of the substantially constant out-of-phase preamble signal; and

a normalizer to normalize a sum of the in-phase preamble samples and a sum of the out-of-phase preamble samples relative to each other to generate an in-phase Doppler estimator and an out-of-phase Doppler estimator.

34. The mobile communications system of claim 33, the transform further comprising a Hilbert Transform.

35. The mobile communications system of claim 33, the first filter further comprising a first low pass filter (LPF) to filter high frequency components from the in-phase preamble signal and the second filter further comprising a second low pass filter (LPF) to filter high frequency components from the out-of-phase preamble signal.

36. The mobile communications system of claim 33, further comprising an analog-to-digital converter to digitize the received preamble signal and data signal.

37. The mobile communications system of claim 33, the received preamble signal and the data signal further comprising GMSK differentially detected signals.

38. The mobile communications system of claim 33, the received preamble signal further comprising a sequence of zeros.

39. The mobile communications system of claim 33, the received preamble signal further comprising a sequence of sixteen zeros.

40. The mobile communications system of claim 33, the received preamble signal further consisting of a sequence of sixteen zeros.

41. The mobile communications system of claim 33, further comprising a Doppler correction circuit, comprising:

a second delay channel coupled to the receiver to generate a delayed data signal based on the data signal;

a second in-phase channel coupled to the receiver and the second delay channel, comprising;

a third multiplier junction to multiply the data signal by the delayed data signal to generate an in-phase data signal;

a fourth multiplier junction to multiply the in-phase data signal by the in-phase Doppler estimator to generate a Doppler corrected in-phase data signal;

a second out-of-phase channel coupled to the receiver and the second delay channel, comprising;

a transform to generate a phase-shifted data signal based on the data signal;

a fifth multiplier junction to multiply the phase-shifted data signal by the delayed data signal to generate an out-of-phase data signal;

a sixth multiplier junction to multiply the out-of-phase data signal by the out-of-phase Doppler estimator to generate a Doppler corrected out-of-phase data signal; and

an adder coupled to the second in-phase channel and the second out-of-phase channel to combine the Doppler corrected in-phase data signal and the Doppler corrected out-of-phase data signal to generate a Doppler corrected data signal.

42. The mobile communications system of claim 41, the second in-phase channel further comprising a third filter to filter the in-phase data signal and the second out-of-phase channel further comprising a fourth filter to filter the out-of-phase data signal.

43. The mobile communications system of claim 42, the third filter further comprising a third low pass filter (LPF) to filter high frequency components from the in-phase data signal and the fourth filter further comprising a fourth low pass filter (LPF) to filter high frequency components from the out-of-phase data signal.

44. The mobile communications system of claim 41, the Doppler correction circuit further comprising a third filter coupled to the second in-phase channel and the second out-of-phase channel to filter the Doppler corrected data signal.

45. The mobile communications system of claim 44, the third filter further comprising a third low pass filter (LPF) to filter high frequency components from the Doppler corrected data signal.